Time Division Multiple Access (TDMA) is perhaps the most popular means of building a digital network composed of many stations. It is the basis of most VSATs as well as the leading digital cellular system, GSM.
Individual earth stations, or VSATs, transmit on the same frequency and so overlap each other (illustrated below:) . However, they are separated in time to preclude them from jamming each other.
A central control station, such as a hub, provides the timing reference and allows new stations to enter the TDMA network. It can also assign blocks of capacity and re-arrange these as needs change.
Example of the time line of a typical TDMA system.
This example of a TDMA system would occupy the entire transponder and allow data transmission speeds of 60 Mbps or more.
More typically, a transponder is divided up in frequency as in FDMA, and one of these frequencies may be for a TDMA access channel. This reduces the transmission speed and therefore the cost of equipment, and dish size as well.